$-\dfrac{2}{8} - \dfrac{3}{10} = {?}$
$ = - {\dfrac{2 \times 5}{8 \times 5}} - {\dfrac{3 \times 4}{10 \times 4}} $ $ = - {\dfrac{10}{40}} - {\dfrac{12}{40}} $ $ = - \dfrac{{10} - {12}}{40} $ $ = -\dfrac{22}{40}$